The role of endorphins during parturition

The concomitant in vivo release of immunoreactive ACTH and beta-endorphin was investigated by measuring the plasma levels of both peptides in the plasma collected during labor and parturition of female human subjects. Maternal and fetal beta-endorphin circulation was investigated by estimating the plasma levels in umbilical vein and artery and comparing them with the maternal plasma content of the peptide. The peptides beta-LPH and epsilon beta-endorphin (which both react with the beta-endorphin antiserum) were separated chromatographically on Sephadex G-50. In the first, and particularly the second stages of labor, levels of both ACTH and beta-endorphin were significantly elevated. The beta-endorphin-like immunoreactivity was also elevated in the umbilical vein and artery, although these values were not as high as in the maternal vein. Neither oxytocin nor the mechanical stress produced by dilatation and curettage played a large role in releasing ACTH and beta-endorphin. The normal pathways of releasing pituitary trophic hormones (disinhibition of inhibitory control of releasing factors in the hypothalamus) must be assumed for the mothers, while fetal production of both beta-endorphin and beta-LPH was demonstrated.